It is known to use a planar ring laser as a gyroscope.
Ring laser gyroscopes typically use a three or four sided laser path. The laser path usually occurs in a lasing chamber which is confined to bores formed in the general configuration of the laser path within a laser housing usually made of highly stable glass or ceramic.
The lasing mirrors are positioned where the laser chamber bores and laser path change direction. The bores extend from mirror to mirror, and the bores are sufficiently large to prevent vignetting of the laser light.
To excite the ring laser to cause two laser paths in opposite directions, it is customary to attach at least one cathode somewhere to the laser housing and to provide anodes on the laser housing together with conduits connecting the anodes and the cathodes into the laser bores in a geometric configuration whereby a motion of ions and electrons between the cathode and anodes excites the laser phenomenon.
Typically, the lasing gas within the bores is a helium-neon mixture at very low pressure. Application of a voltage of sufficient magnitude to ionize the gas between the cathode and anodes is applied to the cathode and to the anodes to cause a migration of electrons from the cathode to the anode and a migration of positive ions from the anodes to the cathode within the gain bores of the lasing gas, thereby exciting the lasing gas. The resonant cavity formed by said mirrors is tuned in frequency by adjusting the laser length for the particular lasing frequency desired. The regions of interaction between the gas and the electrons or ions are designated "gain regions".
It is usually desired that only the TEM.sub.00, or on-axis mode of oscillation be present. To that end, one of the mirrors is apertured to suppress off-axis modes of oscillation in the laser path.
With two laser oscillations occurring at the same time, one with the light travelling in a first direction around the laser path and the other with the light travelling in the other direction around the laser path, it is well known that such a laser may be used as a gyroscope to detect the angular rotation of the laser housing about an axis perpendicular to the plane of the laser paths.
To tune the length of the laser path, it is customary to move one of the mirrors inwardly, perhaps by a screw mechanism or transducer, until the lasing amplitude peaks. The output of the laser, through a partially transmitting one of its mirrors, can be used to servo the position of the tuning mirror.
The laser beam is also typically focused by a large radius preferably spherical mirror to produce a laser beam of substantially uniform cross section. This feature is shown in FIG. 2-4 D of "The Laser" by William V. Smith and Peter P. Sorokin, McGraw-Hill, 1966.